1. Field of the Invention
The present invention relates to a Pb free Ag paste composition for a PDP address electrode and more particularly, it relates to an environment-friendly Pb free Ag paste composition for PDP address electrode that can be applied to a low sintering process not higher than 600° C. and exhibits excellent printing, leveling and sintering performances and of which sintering can be carried out at a sintering target temperature without binder burning off zone.
2. Description of Related Art
In recent, in display devices, as demands on large dimension, high density, high precision and high credibility increase, several pattern processing technologies are being developed and also, researches about compositions for the formation of fine electrodes suitable for the various pattern processing technologies are being actively performed.
As plasma display panels (PDP) have quick response rate and are easy to be manufactured to large dimension compared with liquid crystal panels, they are being currently employed in various fields. In order to form electrodes on the PDPs, in general, patterning methods of electrode materials using screen printing have been used. However, the prior screen printing requires delicate skill and due to low viscosity, pastes on substrates may run down during screen printing and precision by screen declines and accordingly, in screen printing, it is difficult to obtain jumbo screen pattern with high precision required for PDPs. Also, in the prior screen printing methods, open or short by screen might be generated during printing and they required high sintering temperature above 1000° C.
Meanwhile, photolithography methods using photoresist resin compositions have been recently developed to form electrode circuits with high precision suitable for large dimension. They are carried out by forming uniform membranes using photoresist resin compositions dispersed with fine conductive powders, exposing the membranes to light using a mask with desired pattern thereon, and developing desired pattern using development solutions. However, as ordinary photoresist conductive pastes are subject to sintering process above 800° C., such methods are not suitable for the fabrication of PDPs where sintering temperature should be kept below 600° C. because sodium carbonate glass is generally used. If sintering is carried out below 600° C., sintering residues are generated and degradation of conductive properties occurs.
Accordingly, to enable low temperature sintering, Ag electrode pastes for PDP address were prepared using inorganic binders containing Pb of more than 60%. However, such Pb containing pastes contain Pb in a high amount, which is difficult to be recovered after use and hardly degraded in natural conditions due to the inherent characteristics of Pb and accordingly, they may have a serious influence on animals and plants and globe environments.
Although researches about Pb free pastes are in progress to solve such problems, prior Pb free pastes have a sintering temperature above 600° C. Also, as holes are enlarged after sintering, sintering is not completed, and as the organic materials of the photoresist compositions that are not completely removed remain carbonized, Ag powders may not be completely sintered thereby raising electric resistance as an insulator after sintering process and may still create fine cracks on pattern after fine pattern is formed after sintering. Accordingly, in the prior sintering processes, they were kept for 30 to 60 min. at 350° C. before they reached sintering temperature to burn off the organic materials of the photoresist compositions. In other words, in the prior arts, binder burning off zone existed to eliminate the causes bringing about the decrease of the sintering properties such as sintering densification decrease and fine crack formation by the organic materials of the remaining photoresist compositions after sintering, but it resulted in extended sintering time.